1. Field of the Invention
The present invention relates to a method for defining active areas of a substrate, and more particularly, to a method for defining active areas of a substrate and classifying the substrate.
2. Description of the Prior Art
A liquid crystal display (LCD) has advantages of full-color displaying, portability, high resolution, and low radiation. It is for these reasons that the LCD is gradually replacing the CRT monitor in desktop computers. A glass substrate, so-called mother glass, is one of the raw materials for manufacturing LCDs. Glass substrates can be divided into alkali glass and non-alkali glass. The alkali glass is used for manufacturing a twisted nematic (TN) or a super twisted nematic (STN) LCD, while the non-alkali is utilized for fabricating a thin film transistor (TFT) LCD. Generally, before a glass substrate is used for making an LCD, a cleaning process is first performed to clean the glass substrate. Then, the glass substrate is sifted for determining whether the glass substrate is suitable for manufacturing an LCD or not. Finally, active areas of the glass substrate are defined, with an active area being a region of the glass substrate suitable for fabricating an LCD thereon.
In the prior art, when sifting glass substrates, a surface scan apparatus is utilized to inspect the number of defects within a region, which is about 10˜15 mm away from a periphery of a glass substrate. When the number of defects within the region on the glass substrate is larger than an allowable defect count (e.g. 50/piece), the glass substrate is scrapped. Conversely, when the number of defects within the region on the glass substrate is smaller than the allowable defect count (e.g. 50/piece), the glass substrate can be used to manufacture an LCD.
The surface scan apparatus is to utilize an optical analysis technology to inspect defects, such as particles, scratches, breakages, and so on, on the surface of a glass substrate. A light source, beam splitters, reflectors or detectors is used and thus the surface scan apparatus can scan the surface of the glass substrate to inspect the defects on the surface of the glass substrate. As a glass substrate is examined by the surface scan apparatus, the light source projects inspection light beams onto the surface of the glass substrate. When the inspection light beams scan a defect, the inspection light beams are then scattered by the defect. Then, the scattered light beams are received and analyzed by a detector for clarifying and recording a size and a position of the defect. Finally, after the surface scan apparatus finishes scanning the glass substrate, the inspecting results of the glass substrate are recorded in an inspection map, which records distributing positions, counts, and sizes of such defects.
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a schematic diagram showing an inspection map of a glass substrate. FIG. 2 is a schematic diagram of active areas of the glass substrate corresponding to the inspection map shown in FIG. 1. As is known to those skilled in the art, an inspection map of a substrate records positions of defects in numeral type or in graphic type. For convenience of explanation, the inspection map described in the following description records positions of defects in graphic type. That is, the inspection map is marked with a symbol, such as a dot, for illustrating each of the defects on the glass substrate. As a result, the number of the symbols in the inspection map represents the defect counts, while positions of the symbols correspond to the positions of the defects.
As shown in FIG. 1 and FIG. 2, the inspection map 10 corresponds to a surface region of the glass substrate 20, a region 12 corresponds to a region 22, which is inspected by the surface scan apparatus, and a dot 14 represents a defect of the surface region of the substrate. There are forty-six dots 14 in the inspection map 10, which represents that there are forty-six defects on the glass substrate 20. Since the defect count is smaller than 50/piece (i.e. the allowable defect count as described above), the glass substrate 20 can be used for manufacturing an LCD and an active area 24 of the glass substrate 20 can be defined according to the size of the LCD.
In the prior method for sifting a glass substrate suitable for manufacturing an LCD, once the number of defects on the glass substrate is larger than an allowable defect count, the glass substrate is scrapped. Therefore, the prior method for sifting a glass substrate always wastes many glass substrates. For example, as shown in FIG. 3, the number of defects on the glass substrate 20 is 53/piece, which is larger than the above-mentioned allowable defect count of 50/piece. Nevertheless, the number of defects within the whole active areas 24 is 6/piece only, and almost all defects are located outside the active areas 24. Actually, the glass substrate 20 shown in FIG. 3 still can be used for manufacturing an LCD, but in the prior method for sifting a glass substrate, the glass substrate shown in FIG. 3 would be scrapped, which results in wasting glass substrates. Especially, as a size of a glass substrate becomes larger and larger, it is more important to effectively utilize the glass substrate. As a result, it is necessary to look for a suitable method for sifting a glass substrate.